It is common practice to provide several water bars in an entangling drum with internally arranged suction tube, a suction slot in the suction tube that may also consist of several suction openings each being aligned with a respective water bar. The suction tube is subjected to a negative pressure in order to carry off the sprayed-on liquid. The negative pressure acts upon all suction slots of the suction tube. This means that a suction slot whose respective water bar is switched off, is also subjected to the negative pressure. This leads to avoidable pressure losses.